With the development of electronic circuit technologies, particularly microelectronic circuits, which are faster and have denser circuits, there is a continually increasing demand for cooling techniques which can dissipate the continually increasing concentrations of heat produced at the circuit level by integrated circuit chips, microelectronic packages, other components and hybrids thereof. Moreover, such microelectronic circuit technologies require greatly improved heat removal from extremely small circuit components. This situation is worsened when an array of such chips are closely packed to one another. Thus, the density of the chips proportionally increases the heat which must be dissipated effectively by a cooling technique.
In addition to the heat transfer demands on heat exchangers, it is often required that a heat exchanger be designed for a specialized component or use environment, which may involve complex geometries. Such specialized components and environments require specialized heat exchangers.
Cooling techniques have been improved over the recent years in both air cooling applications as well as liquid cooling applications. In either case, it is known to use either cooled forced air or cooled liquid to reduce the temperature of a heat sink device positioned adjacent to the circuit device to be cooled. In another known technique, the circuit chips or packages are cooled by direct immersion cooling, which is the act of directly bringing the chips or packages into contact with the cooling liquid. Thus, no physical walls separate the coolant from the chips. These liquid cooling techniques, either of the heat sink type or direct immersion cooling type, are generally believed to be required in the above described situations with dense very large-scale integration (VLSI) circuits.
One known heat exchanger suitable for use in such an environment is described in U.S. Pat. No. 4,871,623 to Hoopman et al., issued Oct. 3, 1989, which is commonly owned by the assignee of the present invention. The heat exchanger and method described in the Hoopman et al. patent provides a plurality of elongated enclosed electroformed channels that extend through a sheet member between opposing major surfaces. The sheet with the enclosed microchannels is made from a mandrel or master having a plurality of elongated ridges, wherein material is electrodeposited onto the surfaces of the mandrel with the material being deposited on the edges of the ridge portions at a faster rate than on the surfaces defining inner surfaces of the grooves until the material bridges across between the ridge portions to envelope central portions of the grooves and to form the sheet member. Such sheet member includes a base layer with a plurality of elongated projections, each of which extends from the base layer into the grooves of the mandrel, with each of the projections containing an elongated enclosed microchannel. It is also disclosed to then separate the sheet from the mandrel and additionally to use the defined sheet member with its base layer and elongated projections as the mandrel onto which electrodepositing of material again takes place in a similar manner as above thus defining additional elongated enclosed microchannels between the projections of the first formed sheet. The result is a sheet member comprising a microchannel body with a plurality of elongated enclosed channels extending therethrough, wherein the microchannels can have extremely small cross-sectional areas with predetermined shapes.
Another method for producing a suitable heat exchanger comprising a sheet member with a plurality of enclosed microchannels is disclosed in U.S. Pat. No. 5,070,606 issued Dec. 10, 1991, to Hoopman et al., which is also commonly assigned to the assignee of present invention. In this case, the sheet member with the enclosed microchannels is produced by electrodepositing a conductive material about a plurality of fibers with conductive surfaces which are operatively arranged relative to one another to define the enclosed microchannels within the sheet member. Once the electrodepositing step is completed, the fibers are removed by axially pulling the fibers which causes them to experience a reduced diameter as the fibers are stretched during removal from the sheet member. The result is a heat exchanger body having extremely small discrete microchannels passing through the heat exchanger body.
The heat exchangers formed in accordance with the aforementioned Hoopman et al. patents are advantageous in that one piece integrally formed microchanneled heat exchanger bodies are produced. However, both experience a problem in the manifolding of the ends of the microchanneled heat exchanger bodies. In order to manifold these heat exchanger bodies, it is necessary to attach one or both of the open ends of the microchanneled bodies to a tube. The manner of connection has heretofore been accomplished by providing a lengthwise slit in the tubing which accommodates insertion of the open end of the microchanneled body into the interior of the tubing. Then, the joint is silver soldered for sealing the microchanneled body to the tubing. In doing this step, care must be taken so as not to let the solder flow into the ends of the microchannels which could close them.
Other heat exchangers having microchannels which are suitable for cooling electronic circuit components are known which are constructed of plural elements which must be joined together not only to connect a heat exchanger body to a manifold, but also to make up the microchanneled body itself. In one known example, a silicon wafer is fabricated into a microchanneled heat exchanger by sawing into a surface of the silicon with a diamond wafer saw to define a plurality of spaced parallel microgrooves. The silicon wafer is then attached to a substrate which together with the microgrooved wafer define the microchannels. The manifold can be made as a part of the substrate attached to the microgrooved silicon wafer. Other similar heat exchangers including microchannels formed in part by microgrooves made in a silicone wafer or the like are disclosed in U.S. Pat. Nos. 4,450,472, 4,573,067 and 4,567,505 to Tuckerman et al., Tuckerman et al. and Pease et al., respectively. The described manner of forming the microgrooves includes using etching techniques. Additional examples are disclosed in U.S. Pat. No. 4,569,391 to Hulswitt et al., U.S. Pat. No. 4,712,158 to Kikuchi et al., and European Patent application No. EP 0 124 428. Each of these heat exchangers comprise multiple components fabricated into heat exchangers, wherein the plural components are provided in a manner to define the microchannels themselves as well as to make the manifolds.
The present invention specifically relates to the making of a channeled structure by depositing, and more specifically electrochemically depositing, forming material about a sacrificial core, after which the sacrificial core is removed leaving a channeled structure. The general use of sacrificial cores combined with electrochemical deposition is well known. In particular, it is known to electroplate conductive material about sacrificial cores that are inherently conductive as well as sacrificial cores which are rendered conductive by the application of a conductive coating to a non-conductive sacrificial core. Known conductive materials suitable for use as a sacrificial core include those having a low melting point and which are commonly known as fusible metals or alloys. Non-conductive sacrificial cores can be made of various waxes or the like which can be coated with a conductive substance such as silver.
U.S. Pat. No. 4,285,779 to Shiga et al. discloses a fluid circuit device having a base member with a thin sheet integrally electrocast onto the base member, wherein the fluid channels are provided by using a sacrificial core technique. Specifically, strips of soluble substance, such as a low temperature fusing alloy or wax, are applied onto a surface of the base plate. Then, the base plate as well as the strips of soluble material are electroplated. Lastly, the soluble substance is removed leaving an integral channeled circuit device. The fluid circuit device, however, is fabricated as a control device through which fluid signals can be transmitted by way of openings provided through the base member and into the various formed channels, and is not at all concerned with fabricating a heat exchanger and the manifolding of a microchanneled structure. Moreover, the fluid circuit device relies on the base member with precisely located openings as a necessary component of the fluid circuit device.
Other examples of channeled structures made by the electrochemical deposition of conductive material about sacrificial cores which are removed after the electrodeposition step are disclosed in U.S. Pat. Nos. 2,365,690 to Wallace; 2,898,273 to La Forge, Jr. et al.; and 3,445,348 to Aske. These patents are generally related to structures having cavities formed and opened using a sacrificial core technique and are not at all concerned with a heat exchanger connectable to a fluid circuit by a manifold.
A manner for providing orifice openings in an article formed by electrochemical deposition is disclosed in U.S. Pat. No. 3,332,858 to Bittinger. In this case, a removable core is formed out of a silicon material with projections extending from a flat surface thereof which are to be electroplated and by which orifices are to be formed. The surface including the projections is electroplated with conductive material to form the final article which is a spinneret. By plating over the projections, the electroplated material defines protuberances on the outer face of the article which can then be ground away from the article leaving orifices through that face of the spinneret. The core, however, must be wholly removed; so it is necessary that a complete side of the formed article be left open.